1. Field of the Invention
The present invention relates to a facsimile machine which has a security function of selectively permitting or rejecting a facsimile communication depending on a party terminal and also to a security control method for the facsimile machine.
2. Description of the Related Art
A so-called security function is well known as one of service functions of a facsimile machine that allows acceptation of an incoming signal only from a particular party terminal and substantially restricts facsimile communication with facsimile machines other than the particular terminal for the purpose of securing its confidential information.
When it is desired to realize the above security function in a communication system including such sort of prior art facsimile machines, it has been common practice to use such a data as a system password as an index for determining the permission or rejection of a communication between any two of the terminals belonging to the communication system.
More in detail, when a facsimile terminal receives an incoming signal from a network for example, the receiver terminal demands the caller terminal to transmit a system password to the receiver terminal and checks whether or not the system password received from the caller side in response to the demand coincides with a system password previously set in the receiver side.
In the so-called security check, when the received system password coincides with the previously set one, the receiver terminal determines the security check OK and continues its incoming-signal responding operation. When the receiver terminal determines a noncoincidence therebetween or fails to receive the system password from the caller side, on the other hand, the receiver side determines the security check NG and executes its cut-off operation.
In this way, the security function has been conventionally carried out by referring to such an index data as a system password and permitting the communication limited only between the terminals knowing the password.
However, the system password as an index data used in the prior art security control has been set based on uniquely different setting systems employed by different manufacturers. In addition, the transmission format of the system password varies from manufacturer to manufacturer and it is also practically impossible to unify such sorts of index data based on the different specifications of different manufacturers.
For this reason, the security function of this sort of prior art facsimile machine has had a problem that the security function cannot be applied to a large-scale communication system and can be applied only to such a very small-scale communication system that allows communication only between the same manufacturer's terminals.
Further, in the above prior art security control, it is judged as necessary whether or not such an index data as a normal system password has been received from the party terminal and the communication with the party terminal is selectively determined on the basis of the judgement, that is, a security communication pattern is determined depending on whether or not the party terminal knows the system password. In this method, however, in order to change the security communication pattern, the system password must be informed to the corresponding party terminal every time, and thus it is difficult to realize such a truly practical security function that allows flexible change of the security communication pattern according to the convenience of the system.
Furthermore, the prior art facsimile machine is aimed principally at the rejection of an incoming signal from terminals other than the particular terminal and thus is intended to perform its security check only at the time of receiving such incoming signal. In this prior art security control method, since transmission to terminals other than the particular terminal can be freely carried out, the security function is still insufficient from the viewpoint of limiting the facsimile communication only between the particular terminals to prevent any confidence leak.